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What is the endocrine system?

A regulatory system that uses organ glands to regulate the metabolism, growth and development, tissue function, sexual function. reproduction, sleep and mood. It worked the with nervous system, which is another regulatory system.



A ductless gland is a gland that secretes hormones directly into the bloodstream. All endocrine glands are ductless.


What responses do the endocrine and nervous system give?

The endocrine system produces long term effects
The nervous system gives quick, immediate responses


What are the key glands in the endocrine system?

The hypothalamus/pituitary
The thyroid
The parathyroid
The adrenal gland
The pancreas


Describe the hypothalamus/pituitary gland

The hypothalamus is a portion of the brain that directly controls the pituitary gland. The pituitary gland is termed the 'master gland' as it is important for the development and control of the endocrine system.
It is the main link between the endocrine and nervous systems. Produces ADH, FSH and LH.


Describe the thyroid gland

A major gland that wraps around the trachea in a C shape, made up of two joined lobes. The hormone produced (thyroxine, targets the whole body) has particular effect of the heart, respiration, digestions and growth. It influences the enzyme concentration and activity.



Calcitonin is the hormone produced in the C-cells of the thyroid, and released when excessive levels of calcium are detected within bone.


Describe the parathyroid gland

Either side of the thyroid. Important for the balance of calcium/phosphorous. Produces parathromone, which is released if there is not enough calcium detected.
Either on the surface of the thyroid or partially embedded in it.


Describe the adrenal gland

Located slightly above the kidneys on either side. Plays a role in the reproductive system and often surround by fat. Consists of:
- the medulla
- the cortex
Produces adrenaline which increases blood flow to muscles and blood sugar levels.


Describe the pancreas

A secondary endocrine gland that has endocrine and exocrine functions. Produces digestive enzymes and allows glucose to move into cells while ensuring there is not too much.
Produces insulin (controls blood sugar levels - glucose intake up), glucagon (controls blood sugar levels - glucose intake down).


What are the secondary endocrine glands?

The testes, the ovaries, the placenta, the small intestine, liver, thymus and nephron in the kidney



Hormones are organic compounds that target specific organs by acting as chemical messengers. Each target cell has receptor sites specific to certain hormones. They do not make cells do anything new, they just affect the rate at which functions are performed.
Some are secreted fairly constantly, and others in cycles, and some respond to certain stimuli.


What does the response of the cell depend on when targeted by a hormone?

The concentration of the hormone
The number of receptors
The bond between the receptor and the hormone


How are hormones transported around the body?

- they are free in blood transport or bound to plasma
- if the base is lipid soluble, it readily diffuses through capillary walls
- if the base is water soluble it can pass through pores in capillary walls


What is negative feedback?

A system of keeping things within a normal range. It is necessary to keep hormones regulated, as they are not always secreted at the same rate.


What are the 3 main stimuli that control the release of hormones?

1. Humoral stimuli - changes in extracellular fluid e.g. ion concentration
2. Neural stimuli - nerve fibres that stimulate hormone response
3. Hormonal stimuli - a hormone secreted from a different endocrine gland affects another


What hormones are produced in the ovaries?

Oestrogen, progesterone


What hormones are produced in the testes?



What is ADH?

A hormone produced in the pituitary that targets the kidney. It controls blood water levels by triggering water uptake in the kidneys.


What is FSH?

A hormone produced in the pituitary gland that targets the ovaries. It triggers egg ripening and oestrogen production


What is LH?

A hormone produced in the pituitary gland that targets the ovaries. It trigger egg release and progesterone production.


What are the different chemical groups of hormones?

Polypeptides, proteins, amines, steroids